Piezoelectric vibration element and piezoelectric device

ABSTRACT

A piezoelectric vibration element having a favorable drive level characteristic for miniaturization, and a piezoelectric oscillator. The piezoelectric vibration element includes a base made of a piezoelectric material, a plurality of vibration arms extended from the base, a long groove formed along a longitudinal direction of a main surface of each of the plurality of vibration arms, and an exciting electrode provided inside the long groove. A center position in a width dimension of the long groove is decentered in a minus X-axis direction from a center position of an arm width dimension.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Application2005-189680 filed May 6, 2005. The entire disclosure of Japanese PatentApplication No. 2005-189680, filed May 6, 2005 is expressly incorporatedby reference herein.

FIELD

The present invention relates to a piezoelectric vibration element and apiezoelectric device including the piezoelectric vibration element inits package or case.

BACKGROUND

Piezoelectric devices, including a piezoelectric vibration element, apiezoelectric oscillator and the like, have been widely used for smallinformation equipment, such as HDD (hard disc drive), mobile computers,IC cards, and for mobile communications equipment such as cellularphones, car-phones, and paging systems, and piezoelectric gyro sensors,etc.

FIG. 10 is a schematic plan view illustrating an example of apiezoelectric vibration element conventionally used in the piezoelectricdevices.

In the figure, a piezoelectric vibration element 1, whose shape shown inthe figure is formed by etching a piezoelectric material such as quartzor the like, is provided with a base 2 having a rectangular shape, whichis mounted to a package (not shown) or the like, and a pair of vibrationarms 3 and 4, which extends from the base 2 in the vertical direction asviewed in the figure. Long grooves 3 a and 4 a are formed on the mainsurfaces (front and back surface) of vibration arms, and necessarydriving electrodes are formed.

In the piezoelectric vibration element 1, when a driving voltage isapplied via driving electrodes, the vibration arms 3 and 4 perform aflexural vibration so that their distal parts are moved closer and thenapart, resulting in a signal having a given frequency being taken out.

Here, the piezoelectric vibration element 1, in which lead-outelectrodes are formed at the positions indicated as numerals 5 and 6 onthe base 2, is fixed to a base body such as a package or the like withadhesives 7 and 8 applied on the lead-out electrodes.

After fixing and supporting with the adhesive, cut parts 9 are formed tothe base 2 so that the flexural vibration of the vibration arms isprevented from being hindered by a remaining stress caused by thedifferences in the linear expansion coefficient between the material ofthe package or the like, and the material of the piezoelectric vibrationelement.

In the piezoelectric vibration element 1, as a result ofminiaturization, the width W1 of each of the vibration arms 3 and 4 isapproximately 100 μm, the distance MW1 between them is approximately 100μm, and the width BW1 of the base 2 is approximately 500 μm. These partsare miniaturized, so that the length BL1 of the base is accordinglyshortened, thereby the piezoelectric vibration element 1 isminiaturized.

FIG. 11 is a sectional view taken along the line E-E of the vibrationarm 4 in FIG. 10. In the figure, the width of the arm is W1 and excitingelectrodes are not shown. In this regard, the vibration arm 3 also hasthe same sectional view.

The piezoelectric vibration element shows a shape shown in FIG. 12 whenit is further miniaturized.

In a vibration arm 4-1 of the piezoelectric vibration element shown inthe figure, the width dimension MI1 of a long groove 4 a-1 for forming adriving exciting electrode becomes small when the arm width dimension isreduced to the arm width W1-1.

When quartz crystal is wet etched, etching progress is delayed in apredetermined direction due to its etching anisotropy. As a result, aprotrusion or protruded part (hereinafter, called as “fin”) having a finshape shown as indicated as numeral 4 b is produced as an irregularshaped part.

If the arm width W1-1 of the vibration arm 4-1 is determined by takingthe protruded dimension of a fin 4 b into consideration, the arm widthW1-1 is determined smaller. Accordingly, a CI (crystal impedance) valueincreases when a required frequency is adjusted based on the followingformula: frequency (f)=k (coefficient)·W (vibration armwidth)/(1(vibration arm length)×1). Namely, reducing the width of avibration arm for miniaturization results in increasing of CI value.

As for the shape of the vibration arm 4-1 in FIG. 12, the fin 4 b can bereduced when etching time for an outer shape etching of a piezoelectricvibration element is taken for a long time. As a result, field effectcan be improved.

However, in this case, there is a large difference in a dimensionbetween the thicknesses of MK1 and HK1 of walls sandwiching the longgroove 4 a-1 when the width dimension MI1 of the long groove 4 a-1 issmall.

Namely, the difference in a dimension between the thicknesses of MK1 andHK1 of walls sandwiching the long groove 4 a-1 is not much improved dueto a poor circulation of an etchant in a narrow groove width, and ananisotropy in etching.

In this condition, the virtual centerline C passing the center of thewidth dimension MI1 of the long groove 4 a-1 is shifted from the gravitycenter position in the width direction of the vibration arm 4-1.

Accordingly, frequencies may shift to the minus side as shown in FIG. 13when drive level characteristics of a piezoelectric vibration elementare checked. As a result, a piezoelectric vibration element havingfavorable characteristics may not be achieved.

SUMMARY

The present teachings aim to provide a piezoelectric vibration elementhaving a favorable drive level characteristic for miniaturization, and apiezoelectric device.

The aim is achieved by a piezoelectric vibration element that includes abase made of a piezoelectric material, a plurality of vibration armsextended from the base, a long groove formed along a main surface of theplurality of vibration arms, and an exciting electrode provided insidethe long groove. In the piezoelectric vibration element, a centerposition in a width dimension of the long groove is decentered in aminus X-axis direction from a center position of an arm width dimension.

The thicknesses of walls sandwiching the long groove provided to thevibration arm differ due to an anisotropy etching in a process to form apiezoelectric vibration element. The thickness is thicker in the minus Xside. Accordingly, the center position of the width dimension of thelong groove does not coincide with the gravity center position in thewidth direction of the vibration arm when the long groove isconventionally formed at a position. As a result, the flexural vibrationof vibration arms is harmed.

Therefore, a treatment is carried out to reduce or remove an irregularshaped part that is on the side face of each vibration arm and protrudesin a plus X-axis (electrical axis) direction. According to thisstructure, the irregular shaped part produced by an anisotropy etchingis formed so as to be the minimum when the outer shape of thepiezoelectric vibration element is formed by wet etching. This makes theflexural vibration of vibration arms stable.

In addition, by decentering the center position in the width dimensionof the long groove in the minus X-axis direction, i.e. by shifting thecenter position in the width dimension of the long groove in the minusX-axis direction, the center position in the width dimension of the longgroove becomes close to the gravity center position in the widthdirection of the vibration arm. This allows a weight balance of theright and left vibration arms to be adjusted. This also makes itpossible to achieve a stable flexural vibration of vibration arms eventhough a piezoelectric vibration element is miniaturized with a smallgroove width of a long groove, and a fin reduced in size. As a result, apiezoelectric vibration element having an excellent drive levelcharacteristic can be provided.

Another aspect of the present teachings is characterized in that adistance dimension m1 between an outer edge of the long groove and anouter edge of the vibration arm in a plus X-axis direction side islarger than a distance dimension m2 between an outer edge of the longgroove and an outer edge of the vibration arm in a minus X-axisdirection side.

The distance dimension between the outer edge of the long groove formedto the vibration arm and the outer edge of the vibration arm needs to beprovided at both plus and minus X-axis sides, thereby electrodes arereliably polarized. However, this dimension realizes a structure inwhich the center position in the width dimension of the long groove isshifted in the minus X-axis direction by setting the distance dimensionm1 in the plus X-axis side larger than the distance dimension m2 in theminus X-axis side.

Each vibration arm may further include a shrunk width part in which thearm width dimension is gradually shrunk from the base toward a distalside and a changing point P that is in the distal side. From thechanging point P, the arm width dimension is equally continued orincreased toward the distal side, and the changing point P is locatedcloser to the distal side of each vibration arm than an end of the longgroove, in the structure of the first or second invention.

An oscillation with the second harmonic wave can be prevented while CIvalue is suppressed by providing the changing point P when a drivingelectrode (exciting electrode) is formed in the long groove formed tothe vibration arm. The arm width is decreased from the base toward thedistal side. From changing point P, which is in the distal side, the armwidth is increased.

A fourth invention is characterized in that each vibration arm furtherincludes a first shrunk width part in which the arm width dimension issharply reduced toward the distal side from a footing part of eachvibration arm with respect to the base, and a second shrunk width partin which the arm width dimension is gradually reduced further toward thedistal side from an end of the first shrunk width part as the shrunkwidth part.

An oscillation with the second harmonic wave can be prevented while CIvalue is suppressed by providing the second shrunk width part in whichthe arm width dimension is gradually reduced further toward the distalside from an end of the first shrunk width part, and the changing pointP, which is in the distal side and from which the arm width isincreased.

In addition, since the first shrunk width part, in which the arm widthdimension is sharply reduced toward the distal side from the footingpart of each vibration arm with respect to the base, is provided, thestiffness of the footing part can be improved at which the largeststress is applied so as to produce a large strain when vibration armsperform a flexural vibration. This stabilizes the flexural vibration ofvibration arms and suppresses a vibration component in an unwanteddirection, enabling CI value to further decrease. Accordingly, a stableflexural vibration can be achieved in miniaturizing a piezoelectricvibration element, enabling CL value to be lowered.

The piezoelectric vibration element may further include a supporting armthat is extended in a width direction from another end side of the basehaving a predetermined length and extended in a common direction withthe vibration arms outboard the vibration arms, and another end side islocated by the predetermined distance from one side of the base, and thevibration arm extends from the one side of the base, in the structure ofany of the first to fourth inventions.

Where the supporting arm is bonded to a base body such as a package byadhesive bonding or the like, a stress change, which is produced at thebonding position due to the change of surrounding temperature or dropshock or the like, is hardly affected to the vibration arms from thebonding position of the supporting arm through the other end of thebase, and further, through the distance of the given length of the base.As a result, particularly, the temperature characteristic shows well.

Also, in contrast, the vibration leakage from the vibration arms thatperform the flexural vibration is hardly propagated, since the vibrationleakage is reached to the supporting arm spaced apart from the basethrough the given length of the base. Namely, if the length of the baseis extremely short, it can be considered that a situation difficult tobe controlled occurs since a leaked component of the flexural vibrationspreads over the supporting arms. However, such situation is thoroughlyavoided according to the present teachings.

In addition to the advantageous effects, since the supporting arms areextended from the other end of the base in the width direction, andextended in the same direction of the vibration arms at outside of thevibration arms, the whole size can be made compact.

A through hole may be disposed at a position, which is closer to thevibration arms than the connecting part at which the supporting arm isintegrally connected to the base, of the base.

The through hole is disposed at the position, which is closer to thevibration arms than the connecting part at which the supporting arm isintegrally connected to the base. This makes it possible to furthersuppress a vibration leakage without largely lowering the stiffness ofthe base compared to a case in which a cut part is formed deep to theside edge of the base instead of the through hole.

The base may be provided with a cut part formed by reducing the base inthe width direction, in the structure of any of the first through sixthinventions.

The cut part formed by reducing a part of the side edge of the base inthe width direction is provided instead of or in addition to the throughhole. This suppresses a vibration leakage caused by a flexural vibrationof vibration arms to propagate to the connecting part of the supportingarm through the base, thereby increasing CI value can be pretended or bemore reliably prevented.

The cut part may be formed to the base with a distance of 1.2 times ofthe arm width or more from the footing part of each vibration arm, inthe structure of the seventh invention.

The position at which the cut part is provided at a position that ismore than the arm width dimension W2 of the vibration arm from thefooting part of vibration arm in view of the following: there is acorrelation between a region in which a vibration leakage propagates andthe arm width dimension W2 of vibration arms when vibration arms of atuning folk type resonator element perform a flexural vibration.Accordingly, the structure of the cut part can reliably suppress avibration leakage from vibration arms to propagate to the base side. Asa result, a piezoelectric vibration element can be provided which has afavorable drive level characteristic and adequately prevents a leakageof a vibration from vibration arms to the base side.

A piezoelectric device may be provided with a piezoelectric vibrationelement contained in a package or a case, and the piezoelectricvibration element includes a base made of a piezoelectric material, aplurality of vibration arms extended from the base, a long groove formedalong a main surface of the plurality of vibration arms, and an excitingelectrode provided inside the long groove. In the piezoelectricvibration element, a center position in a width dimension of the longgroove is decentered in a minus X-axis direction from a center positionof an arm width dimension.

A compact piezoelectric device can be provided which uses apiezoelectric vibration element that has an excellent drivecharacteristic and can achieve a stable flexural vibration of vibrationarms with a small groove width and a tiny fin in miniaturization by thesame principle of the first invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing a piezoelectric device accordingto one embodiment of the invention;

FIG. 2 is a sectional-view taken along the line A-A of FIG. 1;

FIG. 3 is a schematic enlarged plan view of a piezoelectric vibrationelement used in the piezoelectric device in FIG. 1;

FIG. 4 is a sectional-view taken along the line C-C on the vibrationarms in FIG. 1;

FIG. 5 is a sectional-view taken along the line B-B on the vibrationarms in FIG. 1;

FIG. 6 is a circuit diagram illustrating an example of an oscillationcircuit using the piezoelectric vibration element in FIG. 1;

FIG. 7 is a graph illustrating a drive level characteristic of thepiezoelectric vibration element used in the piezoelectric device in FIG.1;

FIG. 8 is a flow chart illustrating one example of a method formanufacturing the piezoelectric device in FIG. 1;

FIG. 9 shows coordinate axes of a quartz Z plate;

FIG. 10 is a schematic plan view of a conventional piezoelectricvibration element;

FIG. 11 is a sectional-view taken along the line E-E of thepiezoelectric vibration element in FIG. 10;

FIG. 12 is a sectional-view of a vibration arm when a piezoelectricvibration element is miniaturized;

FIG. 13 is a graph illustrating a drive level characteristic of thepiezoelectric vibration element in FIG. 10;

DETAILED DESCRIPTION

FIGS. 1 and 2 show a piezoelectric device according to an embodiment ofthe present teachings. FIG. 1 is a schematic plan view thereof, and FIG.2 is a schematic sectional-view taken along the line A-A in FIG. 1. Inaddition, FIG. 3 is an enlarged plan view to explain the details of apiezoelectric vibration element 32 in FIG. 1. FIG. 4 is a schematicsectional-view taken along the line C-C in FIG. 1. FIG. 5 is a schematicsectional-view taken along the line B-B on vibration arms in FIG. 1.

Referring to the drawings, a piezoelectric device 30 includes apiezoelectric vibration element. The piezoelectric device 30 houses apiezoelectric vibration element 32 in a package 57 serving as a basebody.

The package 57 is formed, for example, in a rectangular box shape asshown in FIGS. 1 and 2. Specifically, the package 57 is formed bylaminating a first substrate 54, a second substrate 55, and a thirdsubstrate 56. For example, it may be formed as follows: a ceramic greensheet made of aluminum oxide is formed as an insulation material; thesheet is formed in a shape as shown in the figures; and then fired.

A through hole 27 for degassing during manufacturing processes isdisposed at the bottom of the package 57. The through hole 27 isprovided with a first hole 25 formed to the first substrate 54, and asecond hole 26 formed to the second substrate 55. The second hole 26 hasan outer diameter smaller than the first hole 25, and communicates tothe first hole 25.

The through hole 27 is sealed by filling a sealing member 28 to make theinside of the package 57 airtight.

The package 57 includes the inner space S formed by removing thematerial inside the third substrate 56 as shown in FIG. 2. The innerspace S is a space for housing the piezoelectric vibration element 32.Positions of supporting arms 61 and 62 of the piezoelectric vibrationelement 32 are placed and bonded to each of the electrode parts 31-1 and31-2 formed on the second substrate 55 with each adhesive 43. On each ofthe positions, a lead-out electrode, which will be described later, isformed.

Since the supporting arms 61 and 62 have the same shape, the supportingarm 61 will be explained referring to FIG. 3. The length dimension u isrequired to be from 60% to 80% of the whole length a of thepiezoelectric vibration element 32 in order to achieve a stablesupporting structure.

In addition, a low stiffness part or structure (not shown), which is,for example, a cut part or shrunk width part, may be disposed at a partof a position between the bonding position of the supporting arm 61 andthe base 51. As a result, reducing a CI value or the like can beexpected.

Further, outside corner parts of the supporting arms 61 and 62 arechamfered in an R-shaped manner, which is convexed outwardly orinwardly, preventing the supporting arms 61 and 62 from being damageddue to a crack, or the like.

The bonding position to the supporting arm, for example, regarding thesupporting arm 61, can be chosen to be only one part corresponding tothe gravity center position G of the length dimension of thepiezoelectric vibration element 32. However, it is preferable that, asshown in the embodiment, the electrode parts 31-1 and 31-2 are chosen tobe two points spaced apart at the same distance from the gravity centerposition located therebetween so as to be bonded. As a result, thebonding structure is further strengthened.

When bonding one supporting arm at one point, it is preferable forachieving a sufficient bonding strength that the length of a region forapplying an adhesive is maintained so as to be 25% or more of the wholelength a of the piezoelectric vibration element 32.

When providing two bonding points as shown in the embodiment, it ispreferable for achieving a sufficient bonding strength that the distancebetween the bonding positions is 25% or more of the whole length a ofthe piezoelectric vibration element 32.

In addition, after fixing and supporting the piezoelectric vibrationelement 32 with the conductive adhesive 43, remaining stress is presentin the base 51. The remaining stress is caused by the difference inlinear expansion coefficient between the materials of the piezoelectricvibration element 32 and the package 57, and the like.

Here, at least one set of the electrode parts 31-1 and 31-2 among theelectrode parts 31-1 and 31-2 is connected to the mounting terminals 41on the backside of the package via conductive through holes and thelike. The package 57 is hermetically sealed in a vacuum by bonding a lid40, which is made of glass and transparent, with a sealing member 58 ina vacuum after housing the piezoelectric vibration element 32. As aresult, frequency can be adjusted by trimming the electrode, or the likeof the piezoelectric vibration element 32 with an irradiation of laserlight from an outside after sealing the lid 40.

A structure may be employed in which the lid 40, which is, for example,a metal plate such as kovar, not a transparent material, is bonded by aseam sealing.

The piezoelectric vibration element 32 is made of quartz, for example.Other than quartz, lithium tantalate, lithium niobate or otherpiezoelectric materials can be used.

In the embodiment, the piezoelectric vibration element 32 is cut from,for example, a single crystal of quartz as described later.

The piezoelectric vibration element 32 is provided with the base 51, anda pair of vibration arms 35 and 36 as shown in FIG. 1. The vibrationarms 35 and 36 are divided in two from one end of the base 51 (the rightend as viewed in the figure) and extended toward the right direction inparallel with each other.

On the front and back surfaces of the main surface of each of thevibration arms 35 and 36, long grooves 33 and 34, which extend in thelongitudinal direction, are preferably formed respectively. As shown inFIGS. 1 and 2, exciting electrodes 37 and 38, which serve as a drivingelectrode, are disposed in the long grooves.

In the embodiment, the distal part of each of the vibration arms 35 and36 is gradually widened in its width as slightly tapered, therebyplaying a role of a plummet with increased weight, as described later.As a result, the vibration arms easily perform a flexural vibration.

In addition, the piezoelectric vibration element 32 extends in the widthdirection of the base 51 from the other end. The other end (the left endas viewed in the figure) is apart from the one end, at which thevibration arms are formed, of the base 51 with the given distance BL2(the length of the base). The piezoelectric vibration element 32 is alsoprovided with the supporting arms 61 and 62 at the positions outside thevibration arms 35 and 36. The supporting arms 61 and 62 extend in thedirection, in which each of the vibration arms 35 and 36 extends (theright direction in FIG. 1), and are in parallel with the vibration arms35 and 36.

Each of the outer shape of the piezoelectric vibration element 32 havinga tuning-fork-like shape and the long groove disposed in each vibrationarm can be precisely formed, for example, by wet etching a material suchas a quartz wafer or the like with a hydrofluoric solution or dryetching it.

As shown in FIGS. 1 and 3, the exciting electrodes 37 and 38 are formedin the long grooves 33 and 34, and the side surface of each vibrationarm. In each vibration arm, the electrode in the long groove and theelectrode formed on the side surface are paired. Each of the excitingelectrodes 37 and 38 is extended to respective supporting arms 61 and 62as respective lead-out electrodes 37 a and 38 a. Accordingly, when thepiezoelectric device 30 is mounted to a mounting substrate or the like,a driving voltage from an outside is applied to each of the lead-outelectrodes 37 a and 38 a in each of supporting arms 61 and 62 via eachelectrode part 31 (31-1 and/or 31-2) from the mounting terminal 41,thereby the driving voltage is applied to each of the excitingelectrodes 37 and 38.

When the driving voltage is applied to the exciting electrode in thelong grooves 33 and 34, electric field efficiency inside the region, inwhich the long groove of each vibration arm is formed, can increase atthe time of being driven.

Namely, as shown in FIG. 5, each of the exciting electrodes 37 and 38 isconnected to an alternating current power supply source with crosswiring. An alternating voltage serving as a driving voltage is appliedto each of the vibration arms 35 and 36 from the power supply source.

Accordingly, the vibration arms 35 and 36 are excited so as to vibratein a phase opposite to each other. In a fundamental mode, i.e. afundamental wave, the vibration arms 35 and 36 are performed a flexuralvibration so that their distal sides are moved closer and then apart.

Here, the fundamental wave of the piezoelectric vibration element 32 is,for example, as follows: Q value is 12000; capacitance ratio (C0/C1) is260; CI value is 57 kΩ; and frequency is 32.768 kHz (“kilo hertz,”hereinafter referred to as kHz).

Also, the second harmonic wave is, for example, as follows: Q value is28000; capacitance ratio (Co/Cl) is 5100; CI value is 77 kΩ; andfrequency is 207 kHz.

Preferably, the base 51 is provided with a concaved part, which isformed by partially shrinking the dimension in the width direction ofthe base 51, or cut parts 71 and 72, at its both side edges. The bothside edges are located sufficiently apart from the end part, which isadjacent to the vibration arms, of the base 51. Each depth of the cutparts 71 and 72 (dimension q in FIG. 3) is preferably set so that itsbottom coincides with the outer side edge of each of the vibration arms35 and 36, which are adjacent to cuts parts 71 and 72 respectively. Forexample, it is about 30 μm.

Accordingly, a vibration leakage is suppressed from being leaked to thebase 51 and being propagated to the supporting arms 61 and 62 when thevibration arms 35 and 36 perform a flexural vibration. As a result, CIvalue can be suppressed at low value.

Increasing the depth dimension of cut parts 71 and 72 lowers thestiffness of the base 51 more than is necessary, even though it iseffective to reduce a vibration leakage, thereby harming stability ofthe flexural vibration of the vibration arms 35 and 36.

Thus, a through hole 80 is provided in the embodiment. The through hole80 is formed at the position that is around the center in the widthdirection of the base 51, and more adjacent to the vibration arms 35 and36 than connecting part 53 at which each of the supporting arms 61 and62 is integrally connected to the base 51.

The through hole 80 is a hole having a rectangular shape and passingthrough the front and back faces of the base 51 as shown in FIGS. 1 and2. The hole shape is not limited, as a round shape, an oval shape, asquare shape, and the like may be employed.

This makes it possible to reduce CI value by further suppressing avibration leakage without largely lowering the stiffness of the base 51compared to forming the cut parts 71 and 72 deep.

Here, the length r of the through hole 80 in the width direction of thebase 51 is preferably about 50 μm. The ratio of the dimension r of thethrough hole 80 and depth q of the cut part 71 to the dimension e,i.e.(r+q)/e, is set from 30% to 80% so as to effective to reduce avibration leakage and influence of the bonded parts through thesupporting arm 61.

In addition, in the embodiment, the distance (dimension p) between theside of the base 51 and the supporting arm 61 or 62 is from 30 to 100 μmin order to miniaturize a package dimension.

Further, in the embodiment, the other end part 53 (connecting part),from which each of the supporting arms 61 and 62 extends, of the base 51is located so as to keep the distance BL2 sufficiently apart from afooting part 52 of the vibration arms 35 and 36 as shown in FIG. 1.

The dimension of the distance BL2 is preferably more than the arm widthdimension W2 of the vibration arms 35 and 36.

Namely, when the vibration arms 35 and 36 of a tuning fork typeresonator element perform a flexural vibration, the area in which thevibration leakage is propagated toward the base 51 has a correlationwith the arm width dimension W2 of the vibration arms 35 and 36. Theinventor focuses attention to this point, having knowledge that theposition serving as a base end of the supporting arms 61 and 62 shouldbe disposed at an adequate position.

Therefore, in the embodiment, the structure can be achieved in which thevibration leakage from the vibration arms 35 and 36 is more surelysuppressed from being propagated to the supporting arms 61 and 62 by thefollowing manner: the part 53 (connecting part), which serves as thebase end of the supporting arms 61 and 62, is chosen so that thedistance from the footing part 52 of the vibration arms to the part 53is more than the dimension corresponding to the size of the arm widthdimension W2 of the vibration arms. Therefore, in order to obtainadvantageous effects of the supporting arms, which will be describedlater, with suppressing CI value, it is preferable that the position of53 is apart from the footing part 52 (i.e. one end part of the base 51)of the vibration arms 35 and 36 by the distance BL2.

Due to the same reason, it is preferable that the positions at which thecut parts 71 and 72 are formed are apart from the footing part 52 of thevibration arms 35 and 36 by the distance that is more than the size ofthe arm width dimension W2 of the vibration arms 35 and 36. Therefore,the cut parts 71 and 72 are formed at the positions, which include apart where the supporting arms 61 and 62 are integrally connected to thebase 51, and are more adjacent to the vibrating arms from the part.

In addition, it was confirmed that a drive level characteristic could beadjusted to a level of a normal piezoelectric vibration element byforming the cut parts 71 and 72 at the positions parted from the footingpart (foot) by 1.2× the arm width dimension W2 or more.

Here, since the supporting arms 61 and 62 are irrelevant to thevibration, no specific conditions are required to the arm width.However, it is preferable that the width is larger than that of thevibration arm in order to assure a supporting structure.

Consequently, in the embodiment, the width BW2 of the base 51 can beachieved to be 500 μm by being composed of the followings: the vibrationarms having the arm width W2 of approximately from 40 to 60 μm; thesupporting arms 61 and 62 having a width of approximately 100 μm; andthe distance MW2 between the vibration arms is approximately from 50 to100 μm. This is nearly the same of the width of the piezoelectricvibration element 1 in FIG. 10, and shorter length. As a result, thismakes it possible to be fully housed in the package having the same sizeas that of the conventional one. The embodiment can obtain the followingadvantageous effects while achieving such miniaturization.

In the piezoelectric vibration element 32 in FIG. 1, since thesupporting arms 61 and 62 are bonded to the package 57 with theconductive adhesive 43, the stress change, which is produced at thebonding position due to the change of surrounding temperature or dropshock or the like, hardly affects the vibration arms 35 and 36 due tothe crooked distance from the bonding position of the supporting arms 61and 62 to the other end part 53 of the base 51, and further the distanceof the length of the base 51, which is more than the distance BL2. As aresult, particularly, the temperature characteristics show well.

In contrast, a vibration leakage from the vibration arms 35 and 36,which perform a flexural vibration, is hardly propagated, since thevibration leakage is reached to the supporting arms 61 and 62 throughthe base 51 with including the given length, which is more than thedistance BL2, of the base 51.

If the length of the base 51 is extremely short, it can be consideredthat a situation difficult to be controlled occurs since a leakedcomponent of a flexural vibration spreads over the supporting arms 61and 62. However, in the embodiment, such situation is thoroughlyavoided.

In addition to the advantageous effects, since the supporting arms 61and 62 are extended from the other end part 53 (connecting part) of thebase 51 in the width direction, and extended in the same direction ofthe vibration arms 35 and 36 at outside of the vibration arms 35 and 36,the whole size can be made compact.

Further, in the embodiment, the tops of the supporting arms 61 and 62are formed so as to be closer to the base 51 than the tops of thevibration arms 35 and 36 as shown in FIG. 1. On this point, the size ofthe piezoelectric vibration element 32 also can be made compact.

Moreover, as compared with the structure of FIG. 10, the followings caneasily be understood. In FIG. 10, the conductive adhesives 7 and 8 areapplied to the lead-out electrodes 5 and 6, both of which are closelylocated. Because of this structure, the bonding process should becarried out by applying the adhesive to extremely narrow area (of thepackage) so that they are not contacted each other for avoiding a short,and by paying attention, even after bonding, not to flow out theadhesive to cause the short before curing it. As a result, the processis made difficult.

In contrast, in the piezoelectric vibration element 32 in FIG. 1, theconductive adhesives 43 are merely applied to the electrode parts 31-1and 31-2 that are respectively located at an approximately intermediateposition of the supporting arms 61 and 62, both of which are spacedapart across the width direction of the package 57. This causes seldomdifficulties described as above, and also no worries of the short.

FIG. 4 is a sectional view of the vibration arm 36 taken along the lineC-C in FIG. 1. Exciting electrodes are omitted for easy illustrating andunderstanding. In this regard, the vibration arm 35 shows the samesectional view (not shown). Only the vibration arm 36 will be explainedto omit a redundant description.

As described above, the long groove 34 is formed to a main surface ofthe vibration arm 36. Namely, in the embodiment, the long groove 34 isrespectively formed on the front surface (upper surface) and the backsurface (lower surface) of the vibration arm 36 so as to extend in thelongitudinal direction. Here, the broken line KL in the figure shows thecenter position in relation to the arm width dimension c of thevibration arm 35.

The piezoelectric vibration element of the embodiment is formed byusing, for example, a quartz wafer, which has a size capable fordividing it into a several number or a many number of the piezoelectricvibration elements 32, as a piezoelectric substrate out of piezoelectricmaterials in a manufacturing process described later. Accordingly, thepiezoelectric substrate is cut from a piezoelectric material, forexample a single crystal of quartz crystal so that X, Y, and Z-axesshown in FIG. 3 become an electrical axis, a mechanical axis, and anoptical axis, respectively since the piezoelectric substrate isprocessed into the piezoelectric vibration element 32 in FIG. 3 throughthe processes. The quartz wafer is achieved by cutting and polishing aquartz Z plate so as to be a given thickness. The quartz Z plate is cutby being rotated within a range of zero to five degrees in clock wiseabout the Z-axis (θ in FIG. 9) in the orthogonal coordinate systemcomposed of the X, Y, and Z-axes when cutting it from the single crystalof quartz.

Regarding the dimension of the thicknesses HK2 and MK2 of wallssandwiching the long groove 34, the dimension of the thickness HK2 ofthe wall, which is located at a minus X-axis side, is larger as shown inFIG. 4. Therefore, the gravity center of the vibration arm 36 isobviously present at the minus X-axis side than the centerline KL.

Accordingly, in the embodiment, the center position of width dimensionof each long groove 34 is decentered to the minus X-axis side comparedto before by changing the position to which each long groove 34 isformed.

The reason is as follows. If the center position in the width directionof the long groove 34 coincides with the center position in the widthdirection of the vibration arm in the vibration arm 36 shown in FIG. 4in a previous manner (refer to FIG. 12), the center in the widthdirection of the long groove 34 does not coincide with the gravitycenter position. As a result, the flexural vibration of vibration armsis harmed.

Accordingly, the center position MC in the width dimension of the longgroove 34 is decentered to the minus X-axis direction. The centerposition MC in the width dimension of the long groove 34 is resultantlylocated closer to the gravity center position in the width direction ofthe vibration arm, thereby a weight balance between the right and leftvibrating arms can be adjusted. This makes it possible to achieve astable flexural vibration of vibration arms even though a piezoelectricvibration element is miniaturized with a small groove width of a longgroove, and a fin 81 reduced in size. As a result, the piezoelectricvibration element 32 having an excellent drive level characteristic canbe provided.

Here, in order to achieve such a structure, a half-etching may becarried out in an etching process (half-etching) of a long groove, whichwill be described later as follows. The half-etching may be carried outafter shifting a mask in the minus X-axis direction by the distance CW,for example, instead of a previous manner in which a half-etching iscarried out so that the center of a region to be half etched coincideswith the centerline KL.

In this case, regarding the dimension of the distance between the outeredge of the long groove 34 formed to the vibration arm 36 and the outeredge of the vibration arm 36, the distance dimension m1 in the plusX-axis side is larger than the distance dimension m2 in the minus X-axisside after forming the long grooves 34 as shown in FIG. 4. Namely, thedistance dimension between the outer edge of the long groove 34 formedto the vibration arm 36 and the outer edge of the vibration arm 36 needsto be surely provided at both plus and minus X-axis sides, therebyelectrodes are reliably polarized. The dimension, however, adequatelyrealizes the above-described structure. In the structure, a position toplace a mask is well designed so that the distance dimension m1 in theplus X-axis side is larger than the distance dimension m2 in the minusX-axis side, thereby the center position in the width direction of thelong groove is shifted in the minus X-axis direction.

Specifically, the dimension m2 in FIG. 4 becomes extremely small, if thegravity center of the vibration arm 36 is adjusted to overlap thecenterline KL by shifting the center position of the long groove 34 inthe minus X-axis direction when the gravity center of the vibration arm36 is present at about 3 μm from the centerline KL in the minus X-axisside. This makes it difficult to polarize electrodes at the part.Accordingly, the long groove 34 is decentered (shifted) in the minusX-axis direction by about from 1 μm to 3 μm, thereby a relatively stableflexural vibration can be achieved without such setback.

FIG. 7 shows a drive level characteristic of the piezoelectric vibrationelement 32 of the embodiment.

In the piezoelectric vibration element 32, a weight balance between theright and left vibration arms can be adjusted by decentering the centerposition in the width dimension of the long groove 34 of the vibrationarm in the minus X-axis direction. As a result, the drive levelcharacteristic shown in FIG. 7 is extremely favorable as is easilyunderstood by referring to FIG. 13.

Next, the preferable detailed structure of the piezoelectric vibrationelement 32 of the embodiment will be explained referring to FIGS. 3 and5.

Since each of the vibration arms 35 and 36 of the piezoelectricvibration element 32 shown in FIG. 3 has the same shape, the vibrationarm 36 will be explained. The vibration arm width c is the widest at thebase end part T at which each of vibration arms is extended from thebase 51. A first shrunk width part TL, which drastically reduces thewidth between the positions of T to U, is formed. The position of T isthe footing part of the vibration arm 36. The position U is apart fromthe position T toward the distal side of the vibration arm 36 with alittle distance. A second shrunk width part, which gradually andcontinuously decreases the width from the position of U to the positionof P, namely, across the distance of CL on the vibration arm. Theposition of U is the end of the first shrunk width part TL. The positionof P is apart from the position of U further toward the distal side ofthe vibration arm 36.

Accordingly, the vibration arm 36 has a high stiffness around thefooting part close to the base by providing the first shrunk width partTL. The vibration arm 36 also has a stiffness continuously decreased byforming the second shrunk width part CL, which is formed from the pointU serving as the end of the first shrunk width part to the top. The partof P is the changing point P at which the arm width is changed. Further,it is a constricted position of the vibration arm 36 from the shapepoint of view. Thus, it also can be expressed as the constrictedposition P. In the vibration arm 36, the arm width extends from thechanging point P to the distal side with the same width, or preferably,with the width gradually and slightly widened as shown in the figure.

Here, the longer the long grooves 33 and 34 in FIG. 3, more increasingthe electric field efficiency of the material forming the vibration arms35 and 36. Here, the longer the long grooves, the lower CI value of thetuning fork type resonator element, at least j/b is up to approximately0.7, where b is the whole length of vibration arm and j is the length ofthe long grooves 33 and 34 from the base 51. Therefore, j/b ispreferably from 0.5 to 0.7. In the embodiment, the whole length b of thevibration arm 36 is, for example, approximately 1200 μm in FIG. 3.

In addition, when the length of the long groove is adequately elongatedto thoroughly suppress CI value, a next arising problem is the CI valueratio (CI value of harmonic wave/ CI value of fundamental wave) of thepiezoelectric vibration element 32.

Namely, if the CI value of a harmonic wave is smaller than the CI valueof the fundamental wave since the CI value of the harmonic wave issimultaneously suppressed by reducing the CI value of the fundamentalwave, oscillation with the harmonic wave easily occurs.

Accordingly, in addition to elongating the long groove to reduce the CIvalue, the changing point P is further provided closely to the top ofthe vibration arm. This allows the CI value ratio (CI value of harmonicwave/CI value of fundamental wave) to be more increased while reducingthe CI value.

Namely, the stiffness of a root part, i.e. in the vicinity of thefooting part, of the vibration arm 36 is strengthen by the first shrunkwidth part TL. This allows the flexural vibration of the vibration armsto be more stable. As a result, the CI value can be suppressed by addingthe advantageous effect of forming the through hole 80.

Since the second shrunk width part CL is provided, the stiffness of thevibration arm 36 is gradually lowered from its footing part, toward thedistal side, to the constricted position P serving as the changing pointof the arm width. From the constricted position P to further the distalside, the stiffness of the vibration arm 36 is gradually increasedbecause the long groove 34 is not provided, and the arm width c isgradually widened.

Accordingly, it can be considered that a “node” of the vibration in thesecond harmonic wave can be shifted to the position closer to the distalside of the vibration arm 36. As a result, lowering the CI value of thesecond harmonic wave cannot be provoked while suppressing the CI valueof the fundamental wave even though the electric field efficiency of thepiezoelectric material is increased by elongating the long groove 34.Consequently, the CI value ratio is almost certainly increased bypreferably providing the changing point P of the arm width closer to thedistal side of the vibration arm from the end part of the long groove asshown in FIG. 3, allowing an oscillation with a harmonic wave to beprevented.

Moreover, according to researches by the inventor, j/b, an arm widthshrunk ratio M, and the CI value ratio corresponding to them arecorrelated, where b is the whole length of the vibration arm, j is thelength of the grooves 33 and 34 from the base 51, M is the ratio of themaximum width to the minimum width of the vibration arm 36, and CI valueratio is the ratio of the CI value of the second harmonic wave to the CIvalue of the fundamental wave.

It was confirmed that an oscillation with a harmonic wave was able to beprevented by the CI value ratio that became more than one by increasingthe arm width shrunk ratio M, which is the ratio of the maximum width tothe minimum width of the vibration arm 36, so as to be more than 1.06 ifj/b is 61.5%.

As a result, the piezoelectric vibration element can be provided thatcan control the CI value of the fundamental wave at low value, and doesnot deteriorate a drive level characteristic even though it is whollyminiaturized.

Next, more preferable structure of the piezoelectric vibration element32 will be explained.

The wafer thickness, i.e. the thickness of quartz wafer forming apiezoelectric vibration element, shown in FIG. 5 as the dimension x ispreferably from 70 to 130 μm.

The whole length of the piezoelectric vibration element 32 shown in FIG.3 as the dimension a is approximately from 1300 to 1600 μm. It ispreferable for miniaturizing a piezoelectric device that the dimensionb, which is the whole length of the vibration arm, is from 1100 to 1400μm, while the whole width d of the piezoelectric vibration element 32 isfrom 400 to 600 μm. Accordingly, in order to miniaturize the tuning forkpart, it is required for ensuring a supporting effect that the widthdimension e of the base 51 is from 200 to 400 μm, while the width f ofthe supporting arm is from 30 to 100 μm.

The dimension k between the vibration arms 35 and 36 in FIG. 3 ispreferably from 50 to 100 μm. If the dimension k is less than 50 μm, itis difficult to sufficiently lessen a fin shaped convex part, which isan irregular shaped part due to an anisotropy in etching, in the plusX-axis direction on the side of the vibration arm shown in FIG. 5 withnumeral 81 when the outer shape of the piezoelectric vibration element32 is formed by wet etching through a quartz wafer, which will bedescribed later. If the dimension k is 100 μm or more, the flexuralvibration of vibration arms may be unstable.

In addition, both dimensions m1 and m2 are from 3 to 15 μm. Each of themis the dimension between the outer edge of the long groove 33 and theouter edge of the vibration arm in the vibration arm 35 (the same as inthe vibration arm 36) in FIG. 5 The electric field efficiency isimproved by the dimensions m1 and m2 of 15 μm or less. The dimensions m1and m2 of 3 μm or more have an advantage to reliably polarizeelectrodes.

The first shrunk width part TL having the width dimension m of 11 μm ormore in the vibration arm 36 in FIG. 3 can be expected to show adefinite effect on suppressing CI value.

In the vibration arm 36 in FIG. 3, it is preferable that the arm widthis widened from the changing point P of an arm width to the distal sideby approximately from 0 μm to 20 μm with respect to the width of thechanging point P of an arm width, which is the position at which the armwidth of the vibration arm 36 is the minimum. Widening the width overthe width described above may deteriorate the stability of a flexuralvibration, since the distal part of the vibration arm 36 is too muchweighted.

An irregular shaped part 81 is formed on one side of the outside of thevibration arm 35 (the same as in the vibration arm 36) in FIG. 5. Theirregular shaped part 81 has a fin shape and is protruded in the plusX-axis direction. This is formed as etching remains due to an anisotropyetching of quartz when a piezoelectric vibration element is wet etchedfor forming its outer shape. In order to achieve a low CI value byincreasing field efficiency, it is preferable that the protruded amountv of the irregular shaped part 81 is reduced within 5 μm by performingthe etching in the etching solution containing hydrofluoric acid andammonium fluoride for from 9 to 11 hours.

It is preferable that the width dimension of the long groove, which isshown as the dimension g in FIG. 3, is approximately from 60% to 90%with respect to the arm width c of the vibration arm in the region, inwhich the long groove is formed, of the vibration arm. The arm width cvaries at the position along the longitudinal direction of the vibrationarm since the first and second shrunk width parts are formed to thevibration arms 35 and 36. The width g of the long groove isapproximately from 60% to 90% with respect to the maximum width of thevibration arm. If the width of the long groove is smaller than this, theelectric field efficiency is lowered, resulting in CI value beingincreased.

Moreover, the end position, which is adjacent to the base 51, of thelong grooves 33 and 34 is preferably the same as the footing part of thevibration arms 35 and 36 as viewed in FIG. 3, i.e. the position of T, oris in the range in which the first shrunk width part TL is present andslightly apart from the position T toward the distal side of thevibration arm, and, particularly, is not preferably in adjacent to thebase end of the base 51 from the position of T.

In addition, the whole length h of the base 51 in FIG. 3, which isapproximately 30% with respect to the whole length a of thepiezoelectric vibration element 32 conventionally, can be achieved to beapproximately from 15% to 25% by employing the cut part, etc., in theembodiment. As a result, the miniaturization is achieved.

FIG. 6 is a circuit diagram illustrating an example of an oscillationcircuit when a piezoelectric oscillator is structured by using thepiezoelectric vibration element 32 of the embodiment.

An oscillation circuit 91 includes an amplifying circuit 92 and afeedback circuit 93.

The amplifying circuit 92 is provided with an amplifier 95 and afeedback resistor 94. The feedback circuit 93 is provided with a drainresistor 96, capacitors 97 and 98, and the piezoelectric vibrationelement 32.

Here, in FIG. 6, the feedback resistor 94 is, for example, approximately10 MΩ (mega ohm). The amplifier 95 can employ a CMOS inverter. The drainresistor 96 is, for example, from 200 to 900 kΩ (kilo ohm). Each of thecapacitor 97 (drain capacitance) and the capacitor 98 (gate capacitance)is from 10 to 20 pF (pico farad).

(Method for Manufacturing a Piezoelectric Device)

Next, an example of a method for manufacturing the piezoelectric devicewill be explained referring to a flow chart in FIG. 8.

The piezoelectric vibration element 32, the package 57, and the lid 40in the piezoelectric device 30 are individually manufactured.

(Method for Manufacturing a Lid and a Package)

The lid 40 is prepared as the lid having a suitable size for sealing thepackage 57 by cutting, for example, a glass plate having a given size.

The package 57 is formed, as above described, by laminating a number ofsubstrates made of aluminum-oxide ceramic green sheets and then firingthe substrates. In the forming, each of the number of substrates isprovided with a given hole inside thereof so as to form the inner spaceS as predetermined when they are laminated.

(Method for Manufacturing Piezoelectric Vibration Element)

First, a piezoelectric substrate is prepared. Then, a given number ofpiezoelectric vibration elements are simultaneously formed from onepiezoelectric substrate by etching their outer shapes (outer shapeetching).

Here, as already described, a quartz wafer having a size capable fordividing it into a several number or a many number of the piezoelectricvibration elements 32 is used from piezoelectric materials as thepiezoelectric substrate.

In the outer shape etching, the piezoelectric substrate exposed as anoutside part from the outer shape of the piezoelectric vibration elementis subjected to the etching of the outer shape of the piezoelectricvibration element by using, for example, a hydrofluoric acid solution asan etchant with a mask such as a corrosion resistant film (not shown).As the corrosion resistant film, for example, a metal film such as goldthat is vapor deposited on chromium serving as an underlayer, or thelike can be used. The etching process varies depending on theconcentration, kind, temperature, and so forth of the hydrofluoric acidsolution.

Here, the wet etching in the outer shape etching process shows thefollowing anisotropic etching to the electrical axis X, mechanical axisY, and optical axis Z shown in FIG. 3 as the etching proceeds.

Namely, the etching rate in X-Y plain of the piezoelectric vibrationelement 32 is follows: in the plus X direction, the progression ofetching is fast in the plain in the direction of 120 degrees withrespect to the X-axis and in the plain in the direction of minus 120degrees with respect to the X-axis; and, in the minus X direction, theprogression of etching is slow in the inside face in the direction of 30degrees with respect to the X-axis and in the inside face in thedirection of minus 30 degrees with respect to the X-axis.

Likewise, the progression of etching speed in the Y direction is fast inthe plus 30 and minus 30 degrees. In the plus Y direction, theprogression of etching speed is slow in the plus 120 and minus 120degrees directions with respect to the Y-axis.

Due to the anisotropy in etching progression, the irregular shaped partprotruded as a fin shape, i.e. “fin” 81 is formed on the outer side ofeach of vibration arms of the piezoelectric vibration element 32 asindicated as the numeral 81 in FIG. 5.

In the embodiment, the fin 81 (irregular shaped part) shown in FIG. 4can be eliminated or reduced in tiny size by the following manner inST11. For example, a quartz wafer having a thickness of about 100 μm isused as a piezoelectric substrate. An etchant is used containinghydrofluoric acid and ammonium fluoride. Etching the quartz wafer withthe etchant for sufficient time period, i.e. for from 9 to 12 hours,particularly for about 11 hours.

In the process, the through hole 80 as well as the outer shape of thepiezoelectric vibration element 32 including the cut parts 71 and 72 aresimultaneously formed. When the process is completed, many piezoelectricvibration elements 32, each of which is connected to the quartz wafer atthe vicinity of the base 51 with a slim connecting part, are achieved astheir outer shapes are completed.

(Half Etching Process for Forming a Groove)

Next, the resist (not shown) for forming a groove remains as a corrosionresistant film at the part to which the groove is not formed so as toleave both wall parts sandwiching each long groove as shown in FIG. 5.Then, the front and back sides of each of the vibration arms 35 and 36are wet etched with the same etching condition of the outer shapeetching so as to form the bottom corresponding to each long groove(ST12).

Here, with reference to FIG. 5, the depth of the groove indicated by thesymbol t is approximately from 30% to 45% with respect to the wholethickness x. As for the t, if it is 30% or less of the whole thicknessx, there can be a case where the electric field efficiency cannotsufficiently be improved. If it is 45% or more, there can be a casewhere a flexural vibration is adversely affected or strength isinsufficient due to the insufficient stiffness.

Here, either of the outer shape etching and the groove etching, or bothof them can be performed by dry etching. In this case, for example, ametal mask is disposed in each time on the piezoelectric vibrationsubstrate (quartz wafer) so as to cover the outer shape of thepiezoelectric vibration element 32, or a region corresponding to a longgroove after forming the outer shape. The piezoelectric substrate withthe mask is, for example, put into a chamber (not shown), and then anetchant gas is supplied at a given degree of vacuum in the chamber so asto produce etching plasma. As a result, dry etching can be performed.Namely, for example, a freon gas cylinder and an oxygen gas cylinder areconnected to a vacuum chamber (not shown), and further an exhaustingpipe is provided to the vacuum chamber so as to vacuum the chamber to agiven degree of vacuum.

When inside the vacuum chamber is vacuum exhausted to a given degree ofvacuum, and freon gas and oxygen gas are supplied and charged to reach agiven pressure of the mixed gas of the two, a direct-current voltage isapplied to generate plasma. The mixed gas containing ionized particleshits the piezoelectric material exposed from the metal mask. Thebombardment mechanically chips away and scatters the piezoelectricmaterial. As a result, etching proceeds.

(Electrode Forming Process)

Next, as a metal serving as the electrode, for example, gold isdeposited on the entire surface by vapor deposition, sputtering, or thelike. Then, the driving electrode described in FIGS. 1 and 5 is formedby photolithography using a resist exposing the part on which theelectrode is not formed (ST13).

Subsequently, weighted electrodes (metal films) 21 are formed on thedistal part of each of the vibration arms 35 and 36 by sputtering orvapor deposition (ST14). The weighted electrodes 21 are not used fordriving the piezoelectric vibration element 32 with applying a voltage,but are utilized for a frequency adjustment described later.

Next, frequency is roughly adjusted on the wafer (ST15). The roughadjustment is the frequency adjustment by a mass reducing method inwhich a part of the weighted electrodes 21 are partially evaporated by airradiation of an energy beam such as laser light.

Subsequently, the slim connecting part connected to the wafer is brokenoff so that an individual piece forming the piezoelectric vibrationelement 32 is provided (ST16).

Then, as described in FIG. 1, the conductive adhesive 43 is applied oneach of the electrodes 31-1 and 31-2 of the package 57. On theconductive adhesives 43, the supporting arms 61 and 62 are placed. Byheating and curing the adhesives, the piezoelectric vibration element 32is bonded to the package 57 (ST17).

Here, the conductive adhesive 43 is, for example, one that is composedof a binder utilizing synthetic resins or the like, and conductiveparticles such as silver particles or the like that are mixed into thebinder, and can simultaneously perform a mechanical connection and anelectrical connection.

If the lid 40 is made of an opaque material such as metal or the like,the through hole 27 described in FIG. 2 is not provided. Then, whileapplying a driving voltage to the piezoelectric vibration element 32 andmonitoring a frequency, the frequency adjustment serving as a finetuning is performed, for example, by the mass reducing method in whichthe distal side of the weighted electrode 21 of the vibration arm 35and/or 36 of the piezoelectric vibration element 32 is irradiated bylaser light (ST18-1).

Subsequently, the lid 40 is bonded to the package 57 by seam welding orthe like in vacuum (ST19-1). After required inspections, thepiezoelectric device 30 is completed.

Alternatively, when the package 57 is sealed with the lid 40, which istransparent, the lid 40 is bonded to the package 57 after bonding thepiezoelectric vibration element 32 in the step of ST17 (ST18-2).

In this case, for example, the heating process is performed in which thelid 40 is bonded to the package 57 by heating a low melting point glassor the like. In this time, gas is produced from the low melting pointglass and the conductive adhesive and the like. Accordingly, the gas isexhausted from the through hole 27 described in FIG. 2 by heating(degassing). Then, a metal ball or pellet made of gold tin, morepreferably, gold germanium, or the like is disposed to a stepped part 29in vacuum, being melt by an irradiation of laser light, or the like. Asa result, the sealing member 28 made of metal in FIG. 2 hermeticallyseals the through hole 27 (ST19-2).

Then, as shown in FIG. 2, the distal side of the weighted electrode 21of the vibration arm 35 and/or 36 of the piezoelectric vibration element32 is irradiated by laser light transmitted through the lid 40 made ofglass, which is transparent and made of such as glass or the like. As aresult, the frequency adjustment serving as a fine tuning is performedby the mass reducing method (ST20-2). After required inspections, thepiezoelectric device 30 is completed.

It should be understood that the invention is not limited to theabove-described embodiments. The structure of each embodiment andmodification example can be appropriately combined or omitted, and anadditional structure not shown can also be combined therewith.

In addition, the invention can be applied to not only the one in whichthe piezoelectric vibration element is housed in a box shaped package,but also to the one in which the piezoelectric vibration element ishoused in a cylindrical package, the one in which the piezoelectricvibration element functions as a gyro sensor, and further to anypiezoelectric devices utilizing a piezoelectric vibration elementregardless the name of the piezoelectric vibration element,piezoelectric oscillator, and the like. Moreover, a pair of vibrationarms is formed in the piezoelectric vibration element 32. However, thenumber of vibration arms is not limited to this, but can be three orfour or more.

1. A piezoelectric vibration element including a base made of apiezoelectric material and a plurality of vibration arms extending fromthe base, the piezoelectric vibration element comprising: a long grooveformed along a main surface of each of the plurality of vibration arms;an exciting electrode provided inside each of the long grooves, whereinan irregular shaped part that is on a side face of each of the pluralityof vibration arms and protrudes in a plus X-axis direction is processedby a treatment to reduce or remove the irregular shaped part and acenter position in a width dimension of the long groove is decentered ina minus X-axis direction from a center position of an arm widthdimension; a shrunk width part in which a width of each arm is graduallyreduced from the base toward a distal end of each of the plurality ofvibration arms; and a changing point P from which the width of each armconstantly increases to the distal end of each arm, the changing point Pbeing disposed between an end of the long groove and the distal end ofeach vibration arm.
 2. The piezoelectric vibration element according toclaim 1, wherein a distance dimension m1 between an outer edge of thelong groove and an outer edge of the vibration arm in the plus X-axisdirection is larger than a distance dimension m2 between an outer edgeof the long groove and an outer edge of the vibration arm in the minusX-axis direction.
 3. The piezoelectric vibration element according toclaim 1, wherein each vibration arm further includes: a first shrunkwidth part in which the arm width dimension is sharply reduced towardthe distal end from a footing part of the vibration arm with respect tothe base; and a second shrunk width part in which the arm widthdimension is gradually reduced further toward the distal end from an endof the first shrunk width part.
 4. The piezoelectric vibration elementaccording to claim 1, further comprising a supporting arm that isextended in a width direction from another end side of the base having apredetermined length and extended in a common direction with thevibration arms outboard the vibration arms, another end side beinglocated by the predetermined distance from one side of the base, thevibration arm extending from the one side.
 5. The piezoelectricvibration element according to claim 4, wherein the base includes athrough hole at a position more adjacent to the vibration arm than aconnecting part in which the supporting arm and the base are integrallyconnected.
 6. The piezoelectric vibration element according to claim 1,wherein the base includes a cut part formed by reducing the base in thewidth direction.
 7. The piezoelectric vibration element according toclaim 6, wherein the cut part is formed to the base with a distance of1.2 times of the arm width or more from a footing part of each vibrationarm.
 8. A piezoelectric device including a piezoelectric vibrationelement contained in a package or a case, the piezoelectric vibrationelement comprising: a base made of a piezoelectric material; a pluralityof vibration arms extended from the base; a long groove formed along amain surface of the plurality of vibration arms; an exciting electrodeprovided inside the long groove, wherein a center position in a widthdimension of the long groove is decentered in a minus X-axis directionfrom a center position of an arm width dimension; a shrunk width part inwhich a width of each arm is gradually reduced from the base toward adistal end of each of the plurality of vibration arms; and a changingpoint P from which the width of each arm constantly increases to thedistal end of each arm, the changing point P being disposed between anend of the long groove and the distal end of each vibration arm.